According to a conventional product storage system for the storage of products (products for storage) of different outline sizes onto a field of a storage warehouse, products of different kinds for storage are stacked and stored kind by kind at predetermined positions on a field plane serving as a storage area, the products of different types being disposed adjacent one another longitudinally and transversely. For carrying out a product of the kind required in the next process from the storage area according to predetermined directions, a transfer device transfers this product onto a pallet which is standing by at a predetermined position of a delivery area, then when a predetermined number of products of the same kind are thus placed onto the pallet, the pallet is carried out from the delivery area and conveyed to the next process (Patent Literature 1).
According to another conventional product storage system, storage areas are disposed respectively on both sides (one on each side) of a conveyor, products on the conveyor are taken out by respective moving mechanisms (transfer devices), then moved and stored in the respective storage areas, and products of the kind required in the next process are carried out from the storage areas according to predetermined directions. In this case, the products are taken out by the moving mechanisms, then are transferred again onto the conveyor and carried out to the exterior of the storage areas (Patent Literature 2).
However, in the storage system described in Patent Literature 1, problems are encountered at the time of carrying out a product from the storage area. More particularly, since a product receiving position of a conveyance device is an arbitrary position around the storage area, the distance between the position of the stored product and the product receiving position is not stable, and in a certain storage condition of the product the distance between the product storage position and the product receiving position becomes longer, resulting in a transfer operation of a long distance. If such a transfer operation becomes more frequent, the time required for the unloading work becomes longer and the efficiency of the unloading work, and hence the efficiency of the storage work, is greatly deteriorated.
A transfer device is used to perform the storage work, the work being product transfer operation between the storage area and the exterior of the storage area. The transfer device is made up of a first transfer device for the transfer of a product to the storage area which product is carried in from the exterior of the storage area (from the preceding process) and a second transfer device for the transfer of a product to an unloading position which product is to be carried out from the storage area to the exterior of the storage area (to the succeeding process). Thus, two separate transfer devices are used, one being dedicated to storage use and the other to unloading use. Therefore, if any one transfer device is turned OFF for maintenance or any other reason, the operation of the other transfer device is limited to a partial operation in the storage area and hence the influence of a decrease of production on the preceding or succeeding process becomes more significant.
In the storage system described in Patent Literature 2, since one storage area is disposed on each side of the product conveyor, the number of products stored in the storage areas is smaller than in the storage system having a conveyor which conveys products via a storage area. Moreover, the transfer device for the transfer of products between each storage area and the conveyor can move in only the range of one storage area, so when the transfer device is turned OFF for maintenance or any other reason, the storage work in one storage area stops completely and hence the efficiency of the storage work is deteriorated markedly.
Further, in each of the storage systems described in both patent literatures, it is only one transfer device that can make access to both loading position of the loading device which is for carrying in products from the exterior of the storage area (from the preceding process) to the storage area and unloading position of the unloading device which is for carrying out products from the storage area to the exterior of the storage area (to the succeeding process). Thus, both conventional storage systems in question are unsuitable for storage of a large quantity of products.    Patent Literature 1: Japanese Patent Laid-Open Publication No. 2000-238906    Patent Literature 2: Japanese Patent Laid-Open Publication No. 2001-031219